Do lightweight flywheels make much difference?

[California98Civic]

Originally Posted by 02ws6

Honda put one of the lightest flywheels used on any D-series engine on the VX engine. Also did the same thing with the crank pulley...

I know this might be tough to answer, but do you know a specific citation for these relative weights? I'd love to know the differences specifically.

[02ws6]

Honda online store : 1995 civic crankshaft - piston parts

Numbers 13 14 and 15 are all obviously different. Do a search for a DX and then the VX. Different part numbers... 14 obviously has less material.. The flywheels were different by only a couple pounds. Like three or 4 if memory serves correct..

[serialk11r]

Some E46 M3 owner had a website where he actually calculated approximately how much moment of inertia the flywheel had and turns out in 1st gear it's quite significant, like strapping a 100 lb weight to your car! I'm getting my flywheel machined when the clutch finally goes.

[fidalgoman]

I can't believe I read every post. Well at least scanned it. It's a balancing act. Heavier flywheels are smoother and lighter ones accelerate faster. At low RPM cruise a stock weight should be much more comfortable but burning off at the stop use a lighter wheel. I suppose bump starts are easier with a lighter unit.

Like everything else there's a range that works and it depends on what we're willing to accept. And like many things we do YMMV.

[YukonCornelius]

I sent Fidanza (aluminum flywheel manufacturer) a lengthy email, this is the response:

Good afternoon,

We unfortunately do not have any hard data tests showing results for gas mileage. Most people who purchase an aluminum flywheel are doing so for the performance aspect of it and do not even consider this portion before making their purchase.

I do apologize that we cannot give you a more definitive answer on this subject and that I could not find any prudent information while researching the subject for you. As you stated in your message I have found a lot of conflicting information as well as a lot of false information mixed in. From my personal knowledge of vehicle operations knowing that the flywheel will reduce the overall rotating mass on the drivetrain it will require less force to put the vehicle in motion but at the same time it will also allow the momentum of the vehicle to slow quicker as well. So it would save on the amount of gas required to begin moving it, but will require a bit more to keep it in motion, this alone may cause any decreased amount of fuel usage to be burned up. On a vehicle that is being driven in more stop and go type situations this may have enough offset to provide an increase overall MPG numbers, while the same vehicle being driven more on the highway may not see any increase and it may possibly see decreases. There are so many outside variables that can affect the mpg, most of these being uncontrollable by the driver it is very hard to say if any particular modification would cause an increase or decrease without being tested in a controlled environment.

From my personnel experiences with usage on my own vehicles, I saw a little gain on a daily driven Honda vehicle but I was not in any way shape or form trying to increase it. I would have days where I would do my best to keep a "light pedal" to help restore mileage but I also had days that it would be more "spirited driving" even with this type of driving i saw an overall increase of about 3-4 MPG on a total tank.

Dan Jenkins
Fidanza Performance
Technical and Product support
tech@fidanza.com

[justme1969]

It is impossible to factor that into just variety and say what the effects are as he said. BUTT> If you P&G it is a definitive upgrade. That is going to be a fact thats easy to distinguish! If it helps wind your car up quicker and uses less energy doing so then Pulse get a kick. My dakota R/t Pulses and glides well but it could also burn a gallon in just waiting at the 14 stop lights on my commute.

[California98Civic]

Here is a page by a guy who seems to know what he is doing and seems to think a lighter flywheel will have a significant effect on vehicle operation:
http://www.jameshakewill.com/clutch-size.pdf

[serialk11r]

Okay that Fidanza person is stupid, it does not take more energy to keep the car rolling with a lighter flywheel.

I'm able to start on steep inclines with only 1100rpm no handbrake, and I "know" my throttle pretty well, I'm just waiting for this clutch to go so I can have a lightweight flywheel put in. It's better in every way except for people who are too lazy to figure out how much throttle to use when starting and let the ECU keep the engine from dying.

[niky]

I guess what he means is that the drivetrain inertia is less, meaning when you let off the gas, you will decelerate quicker. As he's not a hypermiler, he won't be dong P&G like we do.